The invention relates to a rotational body configuration and a method for a web width correction between two printing positions of a rotary printing machine. The printing machine concerned is preferably a wet-on-wet printing machine, in particular an offset printing machine, particularly preferred being a reel-fed rotary printing machine.
In wet-on-wet print rotary printing machines, transverse strain changes occur due to the moistness of the web. This phenomenon, known as fan-out effect, has the undesirable effect that the width of the web, measured transversely to its running direction, varies between two printing nips where the web is printed in sequence. The web, moistened in the one printing nip, swells in its path and becomes wider by the time it reaches the next printing nip. If measures to correct this are not taken, misprints arise in the transverse direction of the web in the printing cylinders forming the printing nips.
One possibility of correcting this, as disclosed, for example, in DE 195 16 368 C2, is to axially adjust the position of the print plates of the plate cylinders which transfer the respective print images on the printing cylinders of the printing nips.
As an alternative to shifting the position of the print plates, it is known to correct the web width. Thus, a device for correcting the fan-out effect on reel-fed rotary printing machines is known from the generic patent specification EP 0 838 420 A2, with which the web is deformed in a wave-like manner transversely to its running direction before entering the subsequent printing nip. The web is guided through two arrays of rolls in the device. The rolls of the one array are arranged staggered to the rolls of the other array transversely to the running direction. As at least one of the two roll arrays is movable into the path of the web, a wave-like profile is imposed on the web, and thus the web width for the print in the subsequent printing nip is reduced.
Comparable devices are known from DE 43 27 646 A1. This document discloses correcting devices comprising rotational body configurations arranged on both sides of the web, and also devices having rotational body configurations arranged only on one side of the web, with which the web is deformed in a wave-like manner transversely to its running direction.
In this device, the web is guided linearly through a number of printing sections, between which a web width correction device is arranged, respectively. This device comprises a number of peripheral projections, laterally spaced away from each other, in the form of rings or brush bodies. Due to the linear web guidance, the web only comes into contact with the peripheral projections, between which the web is freely guided.
WO 99/40006 A1 discloses a guide roll for correcting the side location of webs or also of longitudinal folds. These guide rolls are employed subsequent to the web being printed, whereby the web may also partially wind around the guide roll. The guide roll comprises at least two outer (i.e. near journal of a shaft) expanding elements, which vary in diameter and are located in the region of the ends, the elements being pressurized with pressure means in order to expand. However, guide rolls are not known to be employed for correcting the fan-out effect.
A further device with only local applying of pressure to the web is disclosed in US patent specification U.S. Pat. No. 5,553,542. A number of distanced rolls or compressed air nozzles, the latter being located in the direct vicinity of the web, are provided for applying pressure to the web in order to correct the fan-out effect. Due to the web being guided linearly and vertically, the web partially winds around the pressure application locations only, while otherwise being guided linearly and vertically, however.
Further guide roll means are disclosed in the book of Walewski, Wolfgang: Der Rollenoffsetdruck, Fachschriften-Verlag, 1995, page 94, in German patent specifications DE 33 10 450 C1 and DE 87 03 732 U1, as well as in the European patent specification EP 0 253 981 B1.
In these known devices, the web is guided past the deforming rotational body configurations, decisive web contact only being necessary as a result of web width correction. For this purpose, the rotational body configurations are advanced into the path of the web. Correcting the web width in this way automatically results in the length of the web being changed between the printing nips. Upon printing in the subsequent printing nip, circumferential register errors arise, or circumferential register corrections are required matching the web width correction.
It is an objective of the invention to enable a web width correction which does not require matching circumferential register corrections.
The invention relates to a rotational body configuration for a web width correction between an upstream printing nip and a downstream printing nip of a rotary printing machine, which is preferably a reel-fed newspaper offset rotary printing press. In the two printing nips, in printing production, a web, passing through, is printed in sequence. The rotational body configuration is arranged on one of the two sides of the web and is rotatable in the running direction of the web. In axial direction, it comprises alternatingly juxtaposed radially protruding shell portions and radially retracting shell portions in order to deform the web in a wave-like manner transversely to its running direction.
In accordance with the invention, the rotational body configuration is arranged in a path of the web between the upstream printing nip and the downstream printing nip such that, or the web is guided on its way between the printing nips such that, the web, in the protruding shell portions and in the retracting shell portions, permanently winds around in part the rotational body configuration, i.e. the web permanently contacts not only the protruding shell portions, but also the retracting shell portions throughout the entire printing production. This thus assures neat linear guidance of the web at all times.
In accordance with the invention, for web width correction, a web is not guided past a rotational body configuration, provided for this purpose, which would need to be moved into the path of the web for the purpose of web width correction. In accordance with the invention, the web permanently winds around in part the rotational body configuration. The rotational body configuration in accordance with the invention permanently redirects the web. The web partially winds around the rotational body configuration by at least 3xc2x0, i.e. it is permanently redirected by at least 3xc2x0 by the rotational body configuration. A higher wrap angle of approx. 5xc2x0 or more is preferred. Advantageously, the rotational body configuration is wound around in part by 10xc2x0 or more. The wrap angle may be as much as 180xc2x0.
Due to the invention, one such rotational body configuration may be formed by a single rotational body comprising the protruding shell portions and the retracting shell portions as a non-variable surface shape. The fixed arrangement of such a rotational body, rotatable as a whole, has surprisingly proved to already be sufficient to significantly reverse an expansion of the web such that further web width corrections to achieve a sufficiently good register transversely are not necessary. Adjustments for the width correction, for example, depending on the type of paper and/or web speed is achievable by slightly modifying the longitudinal tension of the web specifically. Preferably, such a rotational body is configured in a wave-like manner at its surface in longitudinal direction. It is particularly preferred that it has concave and convex, or protruding and retracting shell portions continuously merging into the other. The web is in contact with such a rotational body at all times over its full width. The amplitude of the wavy shell surface area, and preferably also the radial distance between the protruding and retracting shell portions of the other example embodiments, is preferably in the range of 0.2 to 3 mm, it preferably amounting to approx. 2 mm.
In preferred example embodiments, the protruding shell portions are radially movable relative to the retracting shell portions, as a result of which the width correction portion can be enlarged, for example by adapting to different paper qualities, web speeds or also by adapting to different printing conditions of the web and thus the different moistenings involved. Due to the relative movement occurring in accordance with the invention between the protruding shell portions and the retracting shell portions, varying web width corrections are already possible solely with one rotational body configuration in accordance with the invention arranged only on one side of the web.
A constant web length between the upstream printing nip and the downstream printing nip is maintained preferably by compensating for the relative movements between the protruding and the retracting shell portions.
In a preferred first embodiment, the protruding shell portions and the retracting shell portions, in a neutral position of the rotational body configuration, comprise a common neutral position axis of rotation. To vary the web width correction, i.e. to adjust the web width, the protruding shell portions are advanced to the web relative to the neutral position axis of rotation and the retracting shell portions are retracted from the web relative to the neutral position axis of rotation mirror-symmetrically in the opposite direction.
Due to this symmetrical adjustment, the mean path of the web between the upstream printing location and the downstream printing location remains the same, despite the adjustment, or is altered with respect to the circumferential register to a degree which is irrelevant practically, i.e. as regards print quality. To keep the length of the web path between the upstream print location and the downstream print location constant, it may also be of advantage to adjust the protruding shell portions and the retracting shell portions asymmetrically in opposite directions with respect to the neutral position axis of rotation. Preferably, given such an asymmetrical adjustment, the protruding shell portions are advanced to the web, relative to the neutral position axis of rotation, to a lesser extent than the retracting shell portions are retracted from the web relative to the neutral position axis of rotation. Preferably, the protruding shell portions, amongst themselves, and the retracting shell portions, amongst themselves, are likewise moved to the same degree during adjustment.
The symmetrical or asymmetrical adjustment may be effected, for example, by radially expanding the protruding shell portions and radially constricting the retracting shell portions. Preferably, the protruding shell portions are formed by an array of rotatively mounted first rolls, and the retracting shell portions are formed by an array of rotatively mounted second rolls.
In a further preferred embodiment, the rotational body configuration comprises a roll body, including eccentric sleeves, non-rotatively mounted thereon, on which cylinder sleeves are rotatively mounted, each independently of the other. Preferably, the eccentric sleeves are designed alternatingly differing in the axial direction of the roll body so that the cylinder sleeves can be advanced to and retracted from the web simply by rotational adjustment of the roll body in order to form protruding and retracting shell portions, preferably alternatingly.
In preferred further embodiments, the rotational body configuration is a roll comprising retracting shell portions, which are radially non-movable relative to the axis of rotation of the roll, and comprising protruding shell portions for advancing relative to the latter.
Advantageously, for compensating changes in the length of the web, which may be caused by movement of the protruding shell portions relative to the retracting shell portions, the rotational body configuration may be arranged radially movable as a whole. A variation of the web width correction may be compensated in this case by a matching radial dislocation of the entire rotational body configuration in the sense of maintaining the web length constant. This radial dislocation is achieved, for example, by mounting the rotational body configuration in eccentric bearings, as is known in principle in printing machine construction for other purposes. The radial movement of the rotational body configuration can also be achieved by means of a linear shifting, instead of a swiveling movement.
In order to adapt the correction of the web width to production requirements, in particular when the rotational body configuration is configured as a roll having a non-variable surface shape, in a further development, several rotational body configurations are rotatively mounted in a rotary cartridge. By rotating the cartridge around an axis of rotation thereof one of the rotational body configurations is brought selectively into a working position, while the other rotational body or bodies of the rotary cartridge remain/s in standby position(s) having no effect on the web. Only the rotational body configuration located in the working position is partially wound around by the web in accordance with the invention. The swivel arm length, formed by the rotary cartridge, may be the same for each of the rotational body configurations of the rotary cartridge. If each of the rotational body configurations is, for example, a rotational body configuration having a non-variable surface shape, and if the amplitude of the shell surface wave is symmetrically varied about its neutral line from one rotational body configuration to the other, then although the waviness imposing the web changes from one rotational body configuration to the next, and thus the set web width also changes, the mean path of the web nevertheless remains the same. Should this assumption not apply to the rotational body configuration of the rotary cartridge, the path of the web between the upstream printing nip and the downstream printing nip can still be maintained constant by selecting the length of the swivel arms, on which the rotational body configurations are mounted relative to their common swivel axis, in coordination with the individual rotational body configurations of the rotary cartridge in the sense of maintaining the web path constant.
Another advantage of the invention is that the rotational body configuration, serving to correct the web width in printing production, can be employed in another printing production as a pure deflection means for a web, which is printed either only in the upstream printing nip in the first printing production or only in the downstream printing nip in the first printing production. Preferably, the rotational body configuration is configured for the advantageous dual purpose so that the protruding and retracting shell portions, if movable relative to each other, can be set to a level relative to the web so that the rotational body configuration provides a smooth straight-cylindrical shell surface area for the web. If the protruding shell portions are cambered, i.e. permanently crowned, as may be the case in accordance with the invention, then the waviness resulting therefrom is so slight that no change in the web width occurs to an extent relevant in practice.
Preferably, in the path of the web between the upstream printing nip and the rotational body configuration or between the rotational body configuration and the downstream printing nip, a deflection means is arranged to guide the web partially winding around the rotational body configuration in accordance with the invention. In the preferred arrangement, the rotational body configuration is used as a guidance to linearly direct the web into the downstream printing nip. In this preferred application, it replaces a printing nip input roll needed in prior art.